Long-Term Soil Responses to Organic Amendments and Biochar: Mechanisms, Soil Health, and Agricultural Sustainability

Organic amendments (composts, manures, crop residues, biostimulants, digestates) and biochar are increasingly positioned as cornerstones of climate-smart soil management. Short-term studies frequently show gains in soil organic carbon, aggregate stability, microbial activity, and crop performance. However, many of these benefits are evaluated over only one or a few growing seasons, providing limited insight into whether they persist, diminish, or evolve over time. Soil systems respond slowly, and the cumulative effects of repeated amendment applications may differ substantially from short-term observations due to changes in organic matter stabilization, nutrient dynamics, microbial succession, and interannual climate variability. The long-term picture is therefore far less settled. How do these amendments behave over 5 to 30+ years across diverse climates, soil types, cropping systems, and management practices? Under what conditions does biochar’s persistence translate into durable carbon storage, and when does it instead prime existing soil organic matter? How do repeated applications reshape nitrogen and phosphorus cycling, micronutrient availability, microbial community succession, and the resilience of these systems to drought, salinity, and warming? And what are the financial, environmental, and agronomic trade-offs associated with sustaining these practices at field and regional scales?

This Research Topic aims to advance understanding of the long-term impacts of organic amendments (e.g., composts, manures, crop residues, and digestates) and biochar on soil health, ecosystem functioning, and agricultural sustainability. We invite contributions based on long-term field experiments, decadal monitoring datasets, meta-analyses, modelling studies, and integrative reviews that move beyond short-term effects to characterise the trajectories, tipping points, and trade-offs of their repeated applications across agroecosystems. We also encourage studies that develop strategies for optimizing amendment type, application rate, timing, and management practices to enhance agronomic and environmental outcomes. By integrating evidence across disciplines, geographic regions, and cropping systems, this Research Topic seeks to identify critical knowledge gaps, improve predictive understanding of long-term soil responses, and provide scientific guidance for developing resilient, climate-smart, and regenerative agricultural systems.

We particularly welcome work linking soil biogeochemistry to climate resilience, nutrient cycling, carbon sequestration, microbial ecology, crop productivity, resilience to climate stress, and policy-relevant carbon accounting. Studies evaluating amendment interactions with management practices, environmental trade-offs, economic feasibility, and ecosystem services are also encouraged. Authors should clearly describe amendment characteristics, application history, experimental duration, and site conditions to facilitate cross-study comparison and improve understanding of long-term soil responses across diverse agroecosystems. Original Research, Methods, Reviews, Perspectives, and Data Reports are all in scope.